Cathode ray tube intensity control system



R. D. OLSON CATHODE RAY TUBE INTENSITY CONTROL SYSTEM Filed Feb. ll, 1960 Oct. l0, 1961 2 Sheets-Sheet 1 Oct. 10, 1961 R. D. oLsoN 3,004,187

CATHODE RAY TUBE INTENSITY CONTROL SYSTEM Filed Feb. ll, 1960 2 Sheets-Sheet 2 llllll. t/Qtzz@ United States Patent O 3,094,187 CATHODE RAY TUBE INTENSITY CONTRL SYSTEM Roland D. Olson, Torrance, Calif., assignor to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Feb. 11, 1960, Ser. No. 8,191 7 Claims. (Cl. 315-22) This invention relates to a system Ifor controlling the intensity of symbols displayed on a cathode r-ay tube and particularly to a system for providing symbols of constant intensity on a time shared display pattern where a single electron beam develops a plurality of symbols representative of information from independent sources.

In some systems such as in radar, many symbols are required to be displayed on the screen of a cathode ray tube having a single electron gun, which symbols may vary in shape, size and number as determined by the source of deflection signals applied to the deflection plates of the tube from separate sources of symbol information. In order to display a plurality of symbols, a time sharing arrangement is provided so that eachY symbol is formed during a dierent portion of a repetitive period with the retentivity characteristics of the phosphor on the screen of the tube retaining a presentation of each symbol while the others `are being formed.

In the prior art, when -a plurality of symbols are displayed on the screen of a cathode ray tube on a time shared basis, the relative intensity of the symbols, which is a function of the number oi electrons striking a particular point on the phosphor of the screen in a given time interval, is set by individually controlling the actual time of write or formation of each symbol. A special gating circuit is provided for intensity setting of each symbol with a selected size and shape by controlling the time of application of each of the dellection signals to the deection plates or the time the electron beam is formed by controlling the blanking pulses applied to the grid of the cathode ray tube `and thus the time of writing of each symbol. However, as each symbol Varies from the size or shape at which the gating circuit is selected as may be required by the information being displayed, the intensity varies because there is no means of adjusting the time of writing as the symbol varies. For example, as a large symbol is made smaller, the intensity of presentation increases and as a small symbol is made larger, the intensity of presentation decreases. It is diflicult for an observer to accurately interpret a plurality of sym-bols when they vary in intensity. Another disadvantage of having a special gating circuit to provide a different time of writing for each symbol is the compleXity of the gating circuitry. A further disadvantage of this prior yart arrangement is that if the deection voltages are removed for any reason, the beam intensity is applied continually to a single position on the screen so that destruction of the phosphor material may occur at such position.

An arrangement that is utilized to control intensity of a symbol on the screen of a cathode ray tube, in systems not having time sharing, differentiates the vertical and horizontal deflection voltages and after rectification of the differentiated voltages combines the rectified signals to -form a signal proportional to the time rate of change of the deection voltages, which signal is applied directly to the intensity grid of the tube. However, in display systems it is preferable to bias the cathode of the cathode ray tube at a low voltage relatiyedtoVV ground mi so that the auxiliary controls such as focus controls and the Aastigmatism controls are at a potential close to ground rather than to have the cathode at ground with the con- Patented Oct. 10, 1961 trols at a high potential. This type of arrangement with the yauxiliary controls at a potential close to ground is especially required in aircraft systems for the safety of the pilot, in which systems time shared displays are often utilized. In order to utilize a very low potential at the cathode, ya coupling capacitor is required between the intensity control circuitry and the intensity grid which is maintained within a few volts or that of the cathode, so that the intensity control circuitry for varying the potential applied to the intensity grid can be operated at a potential relatively close to ground. However, a coupling capacitor prevents certain diderentials of the deflection volt-ages from passing therethrough, such as a sawtooth deflection voltage which has a differential that yis a constant or a D.C. (direct current) voltage. Thus, some symbols cannot be displayed in a reliable manner when a coupling capacitor is utilized. Also, when the differential signals developed from the vertical and horizontal deflection voltages are combined algebraically rather than vectorially, the half wave rectification results in bright spots at certain portions of the symbols.

A display system that provides time sharing for displaying a number of symbols on the screen of the scope and that provides capacitive coupling between the control circuitry and the intensity grid, and that further provides protection against damage to the phosphor in the event of a failure of the deflection voltages would be very valuable to the art.

It is, therefore, -an object of this invention to provide a cathode ray tube intensity control system for use with ya time shared display arrangement in -which the symbols are displayed with uniform intensity regardless of the size, number and shape of the symbols.

It is a further object of this invention to provide an intensity control system 'for a cathode ray tube for time sharing of a plurality of signals from separate sources that utilizes a clamping circuit to prevent destruction of the screen of the cathode ray tube in the Iabsence of de- -ection voltages.

It is a still further object 'of this invention to provide a system for time sharing the writing of -a plurality of symbols on the screen of a. cathode ray tube which differenu'ates the deection voltages, passes the differential signals through full wave rectiiiers and combines the rectied signals `algebraically in a manner to provide symbols of substantially equal intensity.

It is another object of this invention to provide a. system for displaying a plurality of symbols of varying size, shape and number on a cathode ray tube by applying a summed signal indicative of the time rate of change of the horizontal and vertical deflection voltages combined with a carrier Wave through a coupling capacitor arranged Ibetween the intensity control circuitry and the control grid, which system controls the intensity of the symbols when utilizing deflection voltages having a differential value that is a constant.

According to one feature of this invention, a system is provided for Vuse with a time shared display pattern Where several symbols are displayed simultaneously with one electron stream of a cathode ray tube in which all symbol traces are traced at an equal intensity regardless of shape, size or number of the symbols. Horizontal and vertical deection voltages from sources of information to be displayed are applied on a time shared Ibasis not only tothe deection plates of the cathode ray tube but also through ditferentiators to develop signals representing the der-ivative of each ot the dellection voltages. The dierential signals are applied to a full wave rectifierV and then combined in a manner to obtain a signal representing the absolute value of the derivative and the instantaneous intensity requirements of the cathode ray tube. The signals representating the absolute value of the derivative of the deflection voltages are then applied to a summing network which also receives continuous transient blanking gate signals which blank out unwanted portion of the display such as the trace between symbols. The combined signal developed by the summing circuit which includes the intensity information combined with a carr-ier wave is then applied to a clipping circuit to establish a stable unchanging base voltage to which the wave form may be clamped. It is then passed through a coupling capacitor and a clamping circuit which maintains the clipping level at a preselected voltage and is applied to the intensity grid of the cathode ray tube. This clipping and clamping arrangement prevents intensity changes as symbols are added, removed or varied in size and further prevents burning of the screen of the cathode ray tube when the deflection voltages are removed. Thus, the transient blanking signals are utilized as a carrier wave for applying differential signals to the intensity grid, which differential signals may be either alternating or direct current signals.

The novel feature of this invention, as well as the linvention itself, both as to organization and method of operation, will best be understood from the accompanying description taken in connection with the accompanying drawings in which:

FIG. 1 is a combined schematic circuit and block diagram of the intensity control system for a cathode ray tube in accordance with this invention;

FIG. 2 is a schematic diagram to illustrate one example of a plurality of symbols displayed on the screen of the cathode ray tube of FIG. l; and

FIG. 3 is a diagram showing waveforms of time versus amplitude `appearing at various positions in the system of FIG. l.

Referring first to FIG. l, which is a schematic diagram of the intensity control system in accordance with this invention, the general arrangement thereof will be described. A source of vertical deflection signals 1G and a source of horizontal deflection signals 12 are provided to supply vertical and horizontal deflection voltages to a cathode ray tube 14. The sources of deflection signals and 12 may include independent sources of symbol forming information such as range determining circuitry, steering direction circuitry, and artificial horizon determining means, all of which may be included in an aircraft control system, for example. Circuits for developing the signals of the sources of horizontal and vertical deection signals 10 and 12 are well known in the art such as described in Patent No. 2,878,466, Disturbed Lineof-Sight Fire Control System by R. I. Shank et al., issued March l7, 1959. A source of blanking signals 18 is provided to apply gating signals to the sources of deflection signals l@ and 12 through a gating lead 2G so that the deflection signals are obtained from each source of information in the aircraft for a time shared portion of a repetitive period. T'ne source of blanking signals 18 may be a conventional plurality of sequential flip flop divider arrangement that develop a continuous sequence of similarly spaced pulses of equal time dur-ation.

The deflection voltages from the sources 1t? and 12 are respectively applied to a vertical deflection amplifier 24 and a horizontal deflection amplifier 26. The vertical deflection voltages being 180 degrees out of phase from each other are applied from the amplier 24 through leads 30 and 32 to vertical deflection plates 34 and 36 of the cathode ray tube 14. Similarly, the horizontal deflection voltages being 180 degrees out of phase from each other are applied through leads 4@ and 42 to horizontal deflection plates 44 and 46 of the cathode ray tube 14. The verticalV and horizontal deflection voltages in the sources 10 and 12 have a phase relative to each other as determined by the requirements of forming a desired symbol. In response to the deflection voltages, the electron beam developed from an electron gun, which includes a cathode 46, forms a pattern on the phosphor Vofa screen 50 of the cathode ray tube 14, which arrangement is well known in the art.

To provide intensity control of symbols formed on the screen 50, a portion of one of the vertical deflection signals is applied from the amplifier 24 through the lead 30 and through a lead 52 to one plate of a capacitor 54 of a differentiating circuit 56. Also, a portion of one of the horizontal deflection signals is applied from the amplifier 26 through the lead 46 and through a lead 58 to one plate of a capacitor 59 of a differentiating circuit 60. The intensity control system in accordance with this invention utilizes only one deflection voltage for intensity control so that the system is applicable to a system different than shown in FIG. 1, which drives the deflection plates by controlling the voltage applied to only a single plate in either the horizontal or vertical dimensions with the other defiection plate in each dimension connected to a fixed potential. The other plate of the capaoitor 54 is coupled to a lead 64 which, in turn, is coupled to ground through a resistor 66 to provide the differentiating action. Similarly, the other plate of the capacitor 59 is coupled to a lead 68 which in turn is coupled to ground through a resistor 70 to provide the differentiating action. Thus, the differentiating circuits S6 and 69 develop differential signals equal to respectively the rate of change of the vertical and horizontal sweep voltages or the sweep velocity of the electron beam of the cathode ray tube in the vertical and horizontal direction, which signals will be utilized to control the potential on an intensity grid 74 of the cathode ray tube 14.

The differential signals are respectively applied from the leads 64 and 68 to full wave rectifiei's 78 and 80, which are conventional bridge rectier circuits, as well known in the art. In the rectifier circuit 78, positive diiferential signals follow a current path from the lead 64 through a diode 82 coupled to a positive lead 89, through a load resistor 84 and through a diode 86 to ground. Negative differential signals follow a current path from the lead 64 through a diode 88 coupled to a negative lead 85, through the load resistor 84 and through a diode 90 to ground. In a similar manner positive and negative differential signals are applied from the lead 68 to the rectifier 80 and to ground to develop a positive signal on a positive lead 94 and negative differential signals are applied from the lead 68 through the rectifier to develop negative signals on a negative lead 96. Full wave rectication of the differential signals is required because the derivatives of some waveforms such as the negative alternations of a sine Wave are negative.

In order to provide a signal indicative of the absolute value of the differential signals, a summer 98 is provided to separately combine the positive differential signals and the negative differential signals and to combine the absolute value of the positive and negative signals to give a signal proportional -to the instantaneous sweep velocity of the electron beam of the cathode ray tube 14. The positive signals are applied from the leads 89 and 94 through respective resistors 104 and 106 to a lead 110 and to ground through a Ycommon resistor V112. Similarly, the negative differential signals are-applied from the leads and 96 through respective resistors 116 and 118 and to ground through a common resistor 1-12. The common resistors 112 and 122 are tapped resistors having respective movable taps 1,26 and 128 to provide relative intensity adjustment to the system.

The summed positive differential signal is applied from the tap 126 to the grid of a triode 130 of a differential amplifier 132 and the negative summed differential signal is applied from the tap 128 to the grid of a triode 134 also of the differential amplifier 132. The anode of the triode 130 is coupled to a plus 150 volt terminal 136 and the anode of the triode -134 is'coupled to 'the plus 150 volt terminal 136 through a signal forming resistor 1'40. The cathodes of the triodes 130 and 134 are coupled to a minus 15 volt terminal 142 through la common resistor 146. An output lead 148 is coupled between the resistor 140 and the anode of the triode 134 to receive a combined signal representing the sum of the absolute value of the positive signal applied to the grid of the triode 130 and the negative signal applied to the grid of the triode 134. The positive signal at the tap 126 develops a positive response at the cathode of the triode 13G and the negative signal at the tap 128 is etectively inverted and summed with the positive signal to appear as a positive summed derivative signal at the anode of the triode y134.

A summing circuit 152 is provided to combine the summed derivative signal from the lead 148 withV the transient blanking signals from the source 18. The derivative signal and the blanking signals are applied respectively vthrough resistors 154 and 156 to a common point 160 and to ground through a common resistor 162. An alternating combined signal including the blanking signal as the carrier wave for the ydifferential signals is applied from the common point 160 to a clipping circuit 166 which, as will be explained subsequently, determines lan absolute level for clamping operation. The alternating combined signal is applied from the common point 160 to a lead 161 and through the cathode to anode path f a diode 170 for clipping and to an arm 172 of a tapped resistor 174 having one end coupled to a plus 50 volt terminal -176 and the other end grounded. The alternating combined signal, after clipping, is applied from the lead 161 through an ampliiier 180 which is operated class A so that no clipping or limiting occurs therein.

The alternating combined signal is applied from the amplier 180 through a lead 182 to a coupling capacitor 184 so as to isolate a D.C. (direct current) bias of the intensity grid 74 from the control circuitry previously described. The coupling capacitor 184 is part of a clamping circuit 186 which tirmly clamps the clipping level of the combined signal to provide reliable intensity control and to prevent destruction of the screen 50 in the event of a failure of the vertical and horizontal deection signals. The coupling capacitor 184 is coupled to a lead 138 which, in turn, isV coupled through the cathode to anode path of a diode 190 to a movable tap 192 of a tapped resistor 194. One end of the resistor 194 is coupled to a minus 2700 volt terminal 198 and the other end is coupled through a biasing resistor 209' to the cathode 46 of the cathode ray tube 14. A shunting resistor 202 is coupled from the tap 192 to the lead 188 to provide a discharge path for the coupling capacitor 184.

Y Referring now to FIG. 2 which shows the screen 50 of the cathode ray tube 14, as well as to FIG. 1, an example of various symbols which may be time shared will be explained. A range circle 206 may have a diameter which varies to indicate to a pilot the remaining range between his present position and a target, for example, thus varying from a large diameter circle to a very small diameter circle at the center of the screen 50. A steering dot 210 may be provided to indicate to the pilot the direction which he is iiying relative to a calculated position such as a target, which dot is maintained with a constant size. The position 0f the steering dot 210 on the screen 50 relative to the center of the screen 50 may indicate the variation of the flight of a craft utilizing the display from a desired ight path toward a target. A horizon line 212 may be provided to indicate `the attitude of the craft relative to a horizontal position, which line may vary in size and may be utilized only during a portion of a ight.

The system in accordance with this invention may bev utilized with many more signals than indicated on FIG. 2 by using the time sharing arrangement thereof.

Referring now also to FIG. 3 which is a graph of amplitude versus time as well as referring to FIG. 1, the operation of the intensity control system will be further explained. For the display shown in FIG. 2, a period of time to to t6 will be utilized to -form the three symbols, which period is continually repetitive as determined by the source ofV blanking signals 18 and the sources of deection signals 10 and 12 synchronized with the source 18. Between the period t0 and t2, sine wave 216 of a Waveform 217 may be applied from the source '10 to the vertical deection amplifier 24 and similar signals 90 degrees out of phase from the signals 216 may be applied from the source 12 to the horizontal amplier 26 to develop the range circle 206. Between times t2 and t4, the steering dot 210 is formed by a pair ofpsignals such as 218 trom the sources 10 and 12. As is well known, the steering dot 210 is developed by a pair of signals such as 21S having iixed levels `for deecting the electron beam to a desired position on the screen 50. Between times t4 and t6, the horizon line 212 is formed from signals 222 of the waveform 217 from the source 10 and similar signals in phase therewith from the source 12. The signais applied to the amplifiers 24 and 26 are then applied degrees out of phase from each other from the ampliiier 24 to the leads 30 and 32 and similarly from the amplifier 26`to the leads 40 and 42.

The range circle signals 216 are then applied to the differentiation circuit 56 and to the -full wave rectiiier 7 8 to form positive andV negative dilerential signals whose absolute values are summed in the diierential amplifier l132 to form a summed diierential signal 226 of a waveform 225. lIt is to be noted that the summed differential signal 226 has a plurality of amplitude variations indicating the algebraic sum of the rate of change of the vertical and the horizontal deiiection voltages. Because full wave rectitication and summing is provided, this algebraic sum is the instantaneous magnitude, which is .very nearly proportional to the rate of the sweep of the electron beam of the cathode ray tube 14. Thus, variations of intensity due to error of algebraic addition as compared to vectorial addition is greatly minimized so that bright spots on the symbols caused by incorrect algebraic additionv at the peaks of the signals 216, for example, are substantially eliminated. The summed differential signal for the steering dot 210 is a D C. signal 228 having a constant level and the summed differential signal for the horizon line 212 is a signal 232 having instantaneous variations in magnitude resulting from full wave rectiiication and summing of the pair of sine Waves such` as the signal 222.

The gating or blanking signal applied to the summing circuit 152 is shown by -a Waveform 236 and during the time of Writing of each symbol has both a low and a high voltage level. During times to to t1, t2 to t3 and t4 to t5, blanking time is provided for the electron beam to move from one symbol to the other without forming a trace on the screen 50. During times t1 to t2, t3 to t4' and t5 to t6, which are writing times, the symbols are formed on the screen 50. All symbols are retained on the screen 50 because of the retentivity characteristics of the phosphor material. lt is vto be again noted that the gating signal of the waveform 236 may be utilized to control or synchronize the time sharing in the source 10 and 12 of the deflection voltages developed therein. It is to be noted that for blanking out small portions of the symbols such as the range circle 206, the gating signalsrof the waveform 236 between times t1 and t2 may include shortperiod voltage changes between the high andthe low voltage level thereof.

The dierential signal of the waveform 22S and the gating signal of the waveform 236 are thus combined in the summing circuit 152 to form a gated or combined signal of awa-veform 240 which being an A.C. (alternating current) signal will always pass through the coupling capacitor 184. It is to be noted that the difterential signals 228 of the steering dot 210 is a D.C. signal and would be blocked by the coupledrcapacitor 184- so as to prevent intensity control if it were not for combining the diierential information with the alternating gating signal of the waveform 236. 'I'he gated signal of the waveform 240 is applied to the clipping circuit 166 before being applied to the coupling capacitor 184 to positively establish a clipping level 244 so that the gating signal can be reliably clamped at this level. The gated signal of the waveform 240 after clipping is applied through the coupling capacitor 184 to the clamping circuit 186 as a waveform 246 with the clipping level 244 clamped at a desired clamping level 248. The voltage of the clamping level 248 Vis selected so that an electron beam with an intensity controlled by that voltage does not damage the screen 50 when applied continually thereto. Thus, -in the absence of deection voltages the intensity grid 74 is maintained at the clamping level 248 and the electron beam does not have suicient intensity to burn the phosphor on the screen 56. The clamped signal of the waveform 246 is then applied to the intensity grid 74 to control the intensity of the symbols on the screen 50.

Between the times tu to t1, the electron beam projected on the screen Sti with an intensity determined by the clamping level 248 is deilected from a previous symbol to the position of the range circle 206 on the screen 59. The clamping level 248 is selected so that no visible trace of the electron beam is formed on the screen 50. Between the times t1 and L2, the range circle 2% is formed with the instantaneous intensity control voltage of the waveform 246 varying as determined by the full wave rectification and summing operation. Similarly, the steering vdot 216i is formed on the screen 50 during the times t3 to t4 with the intensity control voltage determined by the fixed level of the Waveform 246. Also, the horizon line 212 is formed on the screen 50 during the times t to t6 with the instantaneous varying intensity control voltages of the waveform 246.

In the absence of one symbol such as the horizon line 2,12 during the times I4 to t5, for example, the intensity of the remaining signals remain constant with this system. lf it were not for the clipping and clamping arrangement in accordance with this invention, an average D.C. value would be determined by the number of symbols being Written thus causing the intensity of the symbols on the screen 5l) to vary with the number of symbols presented. The clamping circuit 186 by clamping the gating signal at the clipping level 244 maintains a constant intensity on the screen S0 regardless of the number of signals on the sources lil and 12 that are desired to be displayed. It is again to be noted that the clamping circuit 186 provides absolute protection of the screen 50 during a failure of the deflection voltages, for example, because the clamping level 248 is selected to provide an electron intensity that will not damage the phosphor over any period of time. Further, the clamping level 248 is selected so that the electron beam between one symbol and the other will not form a visible trace on the screen 50.

Thus, there has been described an intensity control system for a cathode ray tube utilizing time sharing for writing a plurality oi symbols with a single electron gun, each symbol having the same Writing time, which system provides symbols of equal intensity regardless of the size, shape and number of symbols displayed. The system provides a reliable means of determining the velocity of' movement of the electron beam so as to minimize the difference between the algebraic sum and the vectorial surn of the rate of change of the vertical and horizontal deection potentials, thus greatly reducing bright spots on the symbols. Further, the system provides a means for positively protecting the phosphor on the screen from burning during the failure of deflection voltages.

What is claimed is:

l. An intensity control system for controlling the intensity grid of a cathode ray tube having horizontal and vertical dellection plates and an electron beam which is time shared during repetitive periods to develop a plurality of symbols each being formed repetitively on a screen during symbol portions of the repetitive periods comprising a source of horizontal and vertical deilection signals coupled respectively to the horizontal and vertical deilection plates, said source controlled so that the deiection signals during each period represent a respective symbol, rst and second diierentiating means coupled respectively to said source of horizontal and vertical deflection signals, first and second full wave rectiers coupled respectively to said rst and second differentiating means, rst summing means coupled to said rst and second rectitiers for developing a summed signal representing the summed absolute value of the differentials of the horizontal and vertical deilection signals, a source of gating signals synchronized with said source of horizontal and vertical Vdeflection signals for dening a blanking period and a writing period during each symbol period, second summing means coupled to said first summing means aid to said source of blanking signals to develop a combined signal, slipping means coupled to said second summing means, an isolating capacitor coupled between said clipping means and the intensity grid, a source of biasing potential, and clamping means coupled between said source of biasing potential and said intensity grid, whereby the potential of said source of biasing potential is isolated from said second summing means and the plurality of symbols are formed on the screen with equal intensity.

2. An intensity control system for a cathode ray tube displaying a plurality of symbols on a screen by forming each symbol during a separate symbol period of a repetitive period with the symbols being retained on the screen by the retentivity characteristics thereof, the cathode ray tube having an electron stream, horizontal and vertical deflection plates and an intensity grid comprising a source of horizontal deection signals, a source of vertical deflection signals, said deflection signals having phase and amplitude characteristics during each symbol period representative of a dilerent one of said plurality of symbols, a horizontal and a vertical deflection amplifier coupled respectively to said source of horizontal and vertical deiection signals and coupled respectively to the horizontal and vertical deection plates, horizontal and vertical differentiation means coupled respectively to said horizontal and vertical amplifiers, horizontal and vertical full wave rectiiiers coupled respectively to said horizontal and vertical dilerentiation means, rst summing means coupled to said horizontal and vertical rectiers for developing a summed signal representative of the sum of the absolute values of the diierential of the horizontal and vertical deflection signals, a source of blanking signals synchronized with said source of horizontal and vertical dellection signals having a blanking level and a Writing level during each symbol period, second summing means coupled to said rst summing means and to said source of blanking signals for receiving said summed signal and the blanking signals to develop a combined signal, a clipping circuit coupled to said second summing means for establishing a fixed clipping level of said combined signal, a coupling capacitor coupled to said clipping circuit for passing the clipped combined signal therethrough, and a clamping circuit coupled between said coupling capacitor and the intensity grid for clamping the clipping level of said clipped combined signal, thereby controlling the intensity of the electron beam so that symbols are presented on the screen with an equal intensity.

3. An intensity control system for a cathode ray tube having an electron beam, an intensity grid, horizontal and vertical deflection plates for receiving during each of a plurality of repetitive symbol periods symbol information for developing a different one of a plurality of symbols, the symbol information being received from a source of horizontal deection signals and from a source of vertical deflection signals, comprising means coupling the source of vertical deection signals and the source of horizontal -deilection signals respectively to the horizontal 3,004,18'? l 9 l0 and vertical deflection plates to cause the electron beam plurality ofA symbols on the screen of a cathode ray tube to be deected in response thereto, iirst and second difhaving an electron beam and an intensity grid, first and ferentiation circuits coupled to said source of deilection second horizontal deflection plates and tirst and second signals for developing rst and second dierential signals vertical deflection plates comprising a source of the horirepresentative of the horizontal and vertical velocity 5 zontal and vertical deection signals-having, during each vectors of the electron beam, rst and second full Wave of a plurality of symbol periods, a phase and amplitude rerectiiiers coupled respectively to said lrst and second lation for developing a respective symbol, rst and second diierentiation circuits for separating positive and negadeflection -amplier means coupled respectively to said tive portions of said iirst and second diierential signals, source of horizontal and vertical deflection signals and iirst Summing meanS Coupled t Said iISt and Second 10 respectively to the horizontal and vertical deection plates, rectier foreconbiningmerneeee'vemefticmresaidmeer rrrsr andrsecomr'ierennaon eiroufscouped rrspec;l and second differential signals, second summing means tively to said rst and second dellection amplifier means coupled to said rst and second rectiiiers for combining for receiving horizontal and vertical deection signals the positive portions of said rst and second differential having a phase relationship similar to that of said Source Signals, third Summing means Coupled to Said first and i of horizontal and vertiea1 deflection signals and for de- SeCond Summing meanS for Combining the abSolnte Value veloping differential signals, rst and second rectiiier cirof Said positive and negative PortionS to form a Snmmed cuits coupled respectively to said first and second dilerensignal representative of the velocity of deflection of said nation circuits for developing positive and negative por` electron bea-m, a Source 0f gating Signals Synchronized tions of the horizontal and vertical diirerentiai signals, with said source of horizontal and vertical deflection rst summing means coupled te said rst and Second recti- Signals, the gating SignalS having a blanling level and a tier circuits for developing a summed signal of the abso- Writing level for eaCh Symbol period; 'fened'"emrm11;`geiute 'valu'ee Vo'e't-he positive arid negative portions of'theV means Coupled to Said third Summing meanS and to said differential signals, a source of blanking signals synchro- Source of gating Signals to develop an a1ternating inten' nized with said source of horizontal and vertical deilecsity control signal, aclipping circuit coupled to said fourth tion signals for developing blanking Signals having a Summing means for eStablishing a predetermined ClippingV blanking level and a symbol writing level during each of level to Said alternating Signal, a Coupling Capaoitor said symbol periods, second summing means coupled to Coupled between said Clipping CirCuit and Said intensity said rst summing means and to said source of blanking gr id, and a Clamping CirCuit Coupled to Said intensity grid signals for developing a combined signal with the summed for maintaining Said Clipping level of Said"alternating"netdierentiasignaiseappearingat tileV blanling levelV and at signal at a predetermined voltage, whereby the intensity of the electron beam is controlled in response to the veloCity of defleCtion thereof and during each symbol clipping said combined signal at a level to remove said Period a Symbol iS formed on the Screen and during each summed signals therefrom from the blanking level thereof, blanklllg Period the electron beam ls deflected t0 e Pesi' 35 a coupling capacitor coupled between ,said clipping circuit tion on said screen for forming a diiierent symbol.

4. A system for developing a plurality of symbols on the symbol writing level of said blanking signals, a clipping circuit coupled to `said second summing means for signal therethrough, a biasing source, and a clamping cir-v the SCreen of a Cathode ray tube by time sharing separate cuit coupled -between said biasing source and said inten- Symbol forming information to be displayed es indi" sity grid for clamping the clipping level of said combined vidual Symbols, the Cathode ray tube having horizontal 40 signal, whereby said biasing source is isolated from said and vertical deflection plates, an electron stream and an clipping Circuit by Said coupling capacitor and Said inte intensity grid Comprising a sourCe of horizontal and Ver sity grid is controlled so Ithat; the symbols developed on the tical deection signals indicative of the separate symbol Screen have substantial equal intensity, forming information, Signal applying Ineens C ouPled be 6. An intensity control system for a cathode ray tube tween said source `and the horizontal and vertical deecto display a plurality of symbols on the screen thereof in tion plates for respectively applying the bonzonlal and response to time shared information, the cathode ray tube vertical deection signals thereto, rst and second diiierenincluding rst andL second hozontal deflection plaes tiation meanS Coupled to said source for respectively le' first yand second vertical dellection plates, an electron beam ceiving a portion of said horizontal and vertical deilecand an intensity control grid comprising a Source 0f help tion Signals to develop differential signals brsi and see' 50 zontal deilection signals, a source of vertical deflection ond reotifying means Coupled respectively to sald first en signals, said horizontal and vertical deflection signals hav- Seoond differentiation means: each 0f seid lecllfylllg ing a phase and amplitude relation representative of said means developing positive and negative portions of said ,plurality of symbols 51st inverting means coupled to Said differential signals, irst summing means coupled to said irSt and Second reotifying meanS for Summing said Pesi' 55 and second horizontal deflection voltages being 180 detive portions second summing means Coupled 'd said fsl grees out of phase from each other, second inverting means and SeCond reetifying means for sum-ming seid negative coupled to said source of vertical deflection signals for deportionS, 'third summing means Coupled t0 said rsl and veloping irst Iand second vertical deflection voltages being second summing means for developing a summed dner- 18,0 degrees out of phase from each other, Sal-d llrst boli. ential signal representative of the absolute value of the Zontal and Vertical deflection voltages having a phase and diierential Signals developed by said first and second amplitude relation similar to that of the horizontal and diierentiating means, a source of alternating signals syn- Vel-tical dellection Signals at said Source, Said first in. chronized with said source of horizontal and vertical de- Vel-ting means being coupled to the rst and second hol-i. ection SignalS, fourth Summing meanS Coupled ioltlllrd zontal deflection plates for applying said rst and second Summing ineens and to seldisourwalielmgnls"ilirzontal deflection voltages thereto to deflect the elecfor developing a Combined alternating signal, ellPPlng tron beam horizontally, said second inverting means being means Coupled to said fourth summing means for estab' coupled to said rst and second vertical deflection plates lishing a predetermined clipping level to said combined for applying Said lll-St and Second Vertical deflection alternating signal, o Coupling eapdeltol" foupled between voltages thereto to deflect said electron beam vertically, a Said Clipping ineans and the intensity grid endelempldg 70 iirst differentiation circuit coupled to said horizontal demeans Coupled to said intensity grid for maintaining seid ilection means for receiving said iirst horizontal dellec- Clipping level at a predetermined level Wbereby the inten' tion voltage to develop a iirst diierential signal representsity of the symbols is maintained substantially constant.

5. An intensity control system for time sharing a plusecond differentiation circuit coupled to said second inrality of symbol information signals to be displayed as a verting means for receiving said rst vertical deflection and the intensity grid for applying the clipped combined v source of horizontal deilection signals for developing .firstV ing rate of horizontal dellection of said electron beam, a Y

voltages to develop a second differential signal representing the rate of vertical deflectiton of said electron beam, a horizontal full wave rectifier coupled -to said 'first differentiation circuit, a vertical full wave rectifier coupled to said 'second diierentiation circuit, a first su'rnming means coupled to said horizontal and vertical rectiti'er for combining negative portions of the rectied rst 'and second differential signals, a second summing means co upied to horizontal and vertical rectiiers for combining the positive portions lof s aid first 'and second dierential signals, differential amplifier means coupled to said rst and vsec'on'd summing means for combining said positive and negative portions to develop a summed signal from 4th'e absolute values 'of said positive `and negative portions, said summed signal represent-ing the Irate of deflection of said 'electron beam, a source of blankin'g signals synchronized with said source of horizontal and vertical deflection signals, third summing means coupled to said differential amplier means and to said source of blanking sighals for developing an alternating signal, a clipping circuit coupled to said third summing means for clipping the lower level of said alternating signal at a preselected clipping voltage, a coupling capacitor coupled to said clipping circuit, a clamping circuit coupled to said coupling capacitor for maintning said clipping level at a preselected clamping voltage, said clamping circuit being coupled to the intensity grid for controlling the intensity of the electron beam in response to the velocity of deflection thereof so as to present the plurality of signals on the screen With equal intensity.

7. An intensity control system for developing a plurality of symbols on the screen of a cathode ray tube and for time sharing information from a source to develop each of the symbols during a diierent symbol period, the cathode ray tube including a screen, an electron stream, an intensity grid, a cathode, and horizontal and vertical de- 'iiection plates coupled to the source for responding to horizontal and vertical deflection signals during each symbol period to deliect the electron stream so as to develop a symbol on the screen `comprising a source of blanking signals having a blanking voltage level and a writing voltage level during each symbol period, iir'st and second differentiation means coupled to said source for developing first and second differential signals indicative of the rate of change of the horizontal and vertical deflection signals, said differential signals having alternating and direct current characteristics, iirst and vsecond full wave rectitiers coupled respectively -to said rst and second diierentiation circuits, first summing means coupled to iirst and Second rectiiiers for developing a summed signal indicative of the absolute value of said rst and second differential signals, second summing means coupled to said source of blanking signals and to said iirst summing means for developing a combined signal utilizing the blanking signals as a carrier Wave, a clipping circuit coupled to said second summing means for establishing a clipping level to said combined signal, a coupling capacitor coupled between said clipping circuit and the intensity grid, a potential source coupled to the cathode of said cathode ray tube, a clamping circuit coupled between said potential source and the intensity grid for maintaining said clipping level at a predetermined clamping level, said coupling capacitor isolating said potential source from said second summing means and said combined signal passing through said coupling capacitor to control the intensity of said symbols when said differential signal has either alternating characteristics or direct current characteristics.

References Cited in the le of this patent UNITED STATES PATENTS 2,700,741 Brown Ian. 25, 1955 2,745,036 Symer May 8, 1956 2,758,247 Johnson Aug. 7, 1956 2,860,284 McKim Nov. l1, 1958 

